Reflex thermoprinting



y 1958 c. s. MILLER ET AL 2,844,733

REFLEX THERMOPRINTING Filed April 2, 1956 source of /J\ rad/4m energy /5 heaf-Jens/f/ue A /4 f py-P p k graph/t origl'flq/ /6 /7 INVENTOPS 64m. 5. MILLEP CAPL A. KUHPMUEP ATTORNEYS United States Patent REFLEX THERMOPRINTING Carl S. Miller, St. Paul, and Carl A. Kuhrmeyer, New Canada Township, Ramsey County, Minn, assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Application April 2, 1956, Serial No. 575,435

4 Claims. (Cl. 250-65) This invention relates to the reproduction of printed matter or the like on heat-sensitive copying-paper by a novel method which for convenience is here termed reflex thermopn'nting. The method involves the application of intense radiant energy in a direction through the copy ing-paper to and from the difierentially reflective surface of the printed page or other graphic subject-matter of which a copy is desired, the conversion of radiant energy to heat energy within the copying-paper in an intensity pattern determined by such subject-matter, and the formation of visible copy in the copying-paper at the highintensity areas of such pattern.

This invention is related to the invention described and claimed in the copending application of Carl S. Miller, Serial No. 747,338, filed May 10, 1947, now Patent No. 2,740,896.

The invention has particular utility in affording means for rapidly obtaining one or more copies of printed matter, diagrams, photographs, or other graphic subjectmatter directly from the original, as in conducting library searches or the like. There is involved merely the proper positioning of the sensitive copy-paper with respect to the original, and the exposure of the original to intense radiant energy through the copy-paper. A true copy is produced directly, without the necessity of subsequent development of a latent image or of other processing. Both negative and positive copies are easily made.

The invention is applicable to the copying of any type of original document carrying visible copy, including painted, inked, or dyed as well as printed or typewritten originals. Messages written in inks of all colors have been copied, as have messages produced by hectographic processes and consisting of organic dyes transferred to white paper.

The attached drawing, which is not necessarily to scale, illustrates in cross-section a strip of heat-sensitive copy-paper associated with a graphic original 11, e. g. a printed page, and irradiated with intense radiant energy from a suitable source 13. The copy-paper is here shown to consist of a radiation-transmissive backing or carrier member 14 and a heat-sensitive layer 15. The printed page has inked portions 16 and ink-free surface areas 17. When the lamp 13 is flashed, there is directly produced in the strip 10 a negative copy of the graphic subject-matter of the original 11; that is, the areas of the heat-sensitive layer above the in-free portions of the surface 17 are visibly changed, as illustrated in the drawing.

The following discussion is offered in probable explanation of the effect just described. It is believed that the radiant energy coming from the source 13 is partially absorbed in the heat-sensitive layer 15, but to an extent insufficient to provide sufiicient heating elfect to cause a visible change. The transmitted portion of the radiant energy impinges on the surface of the original, where portions reaching the inked area 16 are absorbed while portions reaching the ink-free surface 17 are reflected.

The reflected energy is returned to the heat-sensitive coating 15 where a further portion is absorbed and converted to heat energy. The total amount of heat thus provided within the layer 15 raises the temperature at that point to the level required for activating and visibly altering the heat-sensitive layer. The radiation absorbed at the area 16 does not return to the heat-sensitive layer, which at the corresponding area then remains in its original condition. Any heat energy liberated in inked area 16 on absorption of the radiant energy from the lamp 13 is dissipated before it reaches the heat-sensitive layer,

' or is prevented from reaching the layer by the intervening backing member 14 or by other means.

High-intensity photoflash bulbs provide a useful source of high-intensity radiant energy, but other sources having still higher output of radiant energy are preferred. One such source, indicated in the drawing, consists of a Pyrex glass or quartz tube about ten inches long, having an electrode at each end, filled with xenon or other inert gas under reduced pressure, and externally wound with an open wire spiral. The spiral is connected to a 20,000 volt spark coil while the electrodes of the flash tube are connected to an energy storage bank providing a potential of 2600 volts D. C. and capable of applying a 500 watt-second discharge. Activation of the tube, by closing the circuit to the spark coil, results in an intense flash having a duration of about 1000 microseconds, with peak intensity at about 100 microseconds. Intensity is high in the infra-red, and particularly high in the visible, regions.

The flash source just described has been found effective in the copying of all types of graphic subject-matter on rapidly-reactive heat-sensitive copying-paper. One such copying-sheet consists essentially of a thin coating on a transparent thin paper base of a fusible organic iron salt and a reactive phenol in a non-fusing organic film-forming binder. The copying-paper transmits a substantial proportion of the radiant energy and is not visibly changed when exposed to a single flash from the source described. However, the reflection of a substantial portion of the thus transmitted radiation, and the resultant additional absorption of a portion of the reflected energy, as described in connection with the drawing, develops sufficient heat energy in the heat-sensitive layer to make possible the inter-reaction of the reactive components and the production of a visible change.

In one specific example, the copy-sheet consisted of thin map overlay tracing paper coated with a thin layer of a suspension of ferric stearate and gallic acid in a solution of ethyl cellulose. The dry sheet was light tan in color, changing almost instantaneously to a brownish black when heated to -l20 C. When the sheet was placed over a printed page and irradiated as previously described, with the flash lamp at a distance of /2 inch from the paper, a negative copy of the printed area was obtained.

Another specific example of a suitable rapidly-reactive heat-sensitive copying-paper has a sensitive coating of a mixture of gum guaiac and cerium stearate in an ethyl cellulose hinder. Brief heating of such a sheet converts the initial-1y substantially colorless coating to a dark colored modification; further heating causes a further conversion to the colorless state. The sheet is therefore first converted uniformly to the colored modification, inwhich the practice of this invention, the two just described being given as illustrative rather than limitative' examples.

The carrier web may be thin paper as already indicated, but may equally well be transparent film material, e. g. cellulose acetate or ethyl cellulose-film. In any case, the carrier shouldibe capable of'transmitting substantially all of the impressed radiation. The ethyl cellulose or other binder component of thesensitive coating may itself serve as a carrier web when present in sutficient quantity, but in such cases some means of preventing direct'con-tact' between copy-sheet and original is usually found desirable. Thus the copy-sheet may be separated from the original by a thin section of silk bolting-c1othor other-equivalent transparentheat barrier. The extent of such separation must be limited, however, if clear and sharp images are desired, because of excessive d'iflfusion of radiation when the original and the heat-sensitive layer are too widely separated. With sufficiently high intensity and short duration offlash, the heat-barrier layer may be omitted.

Rapidly reactive heat-sensitive compositions are necessary for best results, particularly where the radiant energy flash is of the indicated short duration. A wide variety ofreactive systems are known which are fully effective, thereactants being capable of reacting together even at normal room temperatures but being physically prevented from so reacting at below activation temperatures. Other mechanisms are also available.

The heat-sensitive, layer must be partially absorptive of the radiant energy while still transmitting a substantial proportion of such energy. For example, a layer which absorbs too much of the radiation in a single pass either will be visibly changed over its entire area regardless of the surface beneath, or the amount of radiation remaining for reflection and. further absorption will be inadequate to differentially convert the corresponding areas.

The degree of absorption is easily and exactly cont-rolled by the addition of various pigments or the like to the normally highly transparent heat-sensitive layer;. thus, small amounts of titanium dioxide and of carbon black.

have both proven useful for this purpose where the copysheet in the absence of such materials did not form an adequately visible image due to excessive transmission of the radiant energy; Such pigments are also useful in providing "increased contrastin the final copy.

Another method ofincreasing the absorption of imagecarrying radiant energy in the heat sensitive layer, and" thus increasing the extent of visible change, involves the formation of a reflective grid over the outer surface of the layer, e. g. by printingwith a silver ink. Radiation which passes through theopenings of the grid and. is reflected by the more reflective areas of the original is in part' re-. reflected by the grid into the heat-sensitive layer to increase still further the development of heat energy at such areas.

The elfectiveness of the copying process depends also on the intensity of. the radiant energy. For example, a copy-sheet which does not provide an effective, copy with a particular source of energy may be found fully eflective if the energy level is substantially increased. With increased energy,.the distancebetween lamp and sheet may be increased, therebyv permitting duplication over somewhat wider areas. Radiant energy absorbed in the absorbent printed areasof certain originals and converted toheat energy is more rapidly dissipated and prevented from affecting, the image-forming layer whenthe radiant 1. A method for the, production of permanent facsimile copies of a graphic original having a visible graphic pattern on avisibly contrasting background, said pattern and background being. differentially reflective of intense radiant energy, said method comprising placing over the graphic original a heat-sensitive rapidly-reactive copypaper capable of absorbing a substantial proportion of said. energy, and. irradiating the original through the copy-paper with. said.- intense radiantenergy. atsufliciently. high intensity and for sufliciently. short time to provide a visible change .in the areas=of 'the-copy-paper correspond.- ing to the more reflective. areas of theoriginal while avoiding visible change in, areas, corresponding to the lessreflective areas.

2. A methodfor the production of permanent facsimile copies of a graphic. original having a visible graphic.

patternon avisibly. contrasting background, said pattern and background being diiferentially reflective of intense radiant energy, said method comprising: (a) placing over: the graphic. original a copy-paper consisting essene tially of a. rapidly-reactive. heat-sensitive layer and an associated 'thin transparent carrier, saidheat-sensitive layer being. capable of absorbing a substantial proportion of ,said energy and. said copy-paper being placed with the carrier web. in contact, with thegraphic original; and (b) irradiating the original. through the copy-paper with said intense, radiant energy at sufiiciently high intensity and for sufliciently. short time to provide a visible change in the areas. of the heat-sensitive layer corresponding to the more reflective areasof, the original while avoiding visible change in areas corresponding to theless reflective areas.

3. Amethod forthe production of permanent facsimile; copies of a graphic original having a: visible graphic pattern on a visibly contrasting background, said patternandbackground being differentially reflective of intense radiant energy, saidmethod comprising: (a) placing.

over-the. graphic, original a copy-paper having a rapidlyreactive. heat-sensitive layer, said heat-sensitive layer being; capable, of. absorbing a. substantial proportion: of said:v

energy. and being prevented from directly contacting. the graphic original by an intervening thin transparent heatinsulative fibrousv sheet material; and (b)-irradiating the original through the copyfpaper. with said intense radiant energy at suificiently high intensity and for sufliciently short time toprovideavisible change in the areas of the heat-sensitive layer. corresponding to the more reflective areas ofthe original While. avoiding visible change in areas corresponding to the lessvreflective areas.

4.- The method of copying as defined in claim 3 in which the thin fibrous-sheet materialisa separate thinweb.

References Cited inithe file of this patent UNITED STATES PATENTS Miller Apr. 3; 1956. Miller Apr. 3, 1956' 

1. A METHOD FOR THE PRODUCTION OF PERMANENT FACSIMILE COPIES OF A GRAPHIC ORIGINAL HAVING A VISIBLE GRAPHIC PATTERN ON A VISIBLY CONTRASTING BACKGROUND, SAID PATTERN AND BACKGROUND BEING DIFFERENTIALLY REFLECTIVE OF INTENSE RADIANT ENERGY, SAID METHOD COMPRISING PLACING OVER THE GRAPHIC ORIGINAL A HEAT-SENSITIVE RAPIDLY-REACTIVE COPYPAPER CAPABLE OF ABSORBING A SUBSTANTIAL PROPORTION OF SAID ENERGY, AND IRRADIATING THE ORIGINAL THROUGH THE COPY PAPER WITH INTENSE RADIANT ENERGY AT SUFFICIENTLY HIGH INTENSITY AND FOR SUFFICIENTLY SHORT TIME TO PROVIDE A VISIBLE CHANGE IN THE AREAS OF THE COPY-PAPER CORRESPONDING TO THE MORE REFLECTIVE AREAS OF THE ORIGINAL WHILE AVOIDING VISIBLE CHANGE IN AREAS CORRESPONDING TO THE LESS REFLECTIVE AREAS. 